1. Field of the Invention
This invention relates generally to telephone communication systems employing bidirectional voice frequency repeaters and more particularly, it relates to an enhanced line powered amplifier which functions as a bidirectional voice frequency repeater, having automatic gain adjustment circuitry and manual balancing circuitry.
2. Description of the Prior Art
Recent advances in line power amplifiers for enhancing signals in a two-wire bidirectional transmission path in telephone systems include power derivation circuitry for deriving power from the transmission lines, automatic gain adjustment for automatically setting the gain to a fixed level and automatic balancing circuitry for automatically adjusting the balance networks on both the cable side (typically the telephone central office) and equipment side (e.g., the subscriber equipment).
U.S. Pat. No. 4,961,218 to Kiko discloses an enhanced line power amplifier with the above advances. The amplifier as disclosed in the '218 patent performed well for a variety of voice grade two-wire special service circuits requiring transmission treatment including Centrex, PBX-CO trunks, WATS lines and analog data lines. The disclosure of U.S. Pat. No. 4,961,218 is incorporated by referenced herein.
For applications in which the cable side device also includes automatic balancing circuitry, such as in high speed modem circuits, a problem may arise when the automatic balance circuit in the modem and the automatic balance circuit in the amplifier simultaneously attempt to balance the cable between them, resulting in an unstable operating condition.
Therefore, a need exists for an amplifier which includes a manual adjustment to its impedance for balancing itself to the network.
Another desirable feature in repeater amplifier applications is the provision in the amplifier for remote testing and alignment, which facilitates off-site testing of the amplifier by the cable side or central office equipment.